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    <title>Document</title>
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    <script>
      const arr = ['a', 'b', 'c'];
      console.log(Object.keys(arr)); //['a', 'b', 'c']

      const obj = { 0: 'a', 1: 'b', 2: 'c' };
      console.log(Object.keys(obj)); //['a', 'b', 'c']

      const anObj = { 100: 'a', 2: 'b', 7: 'c' };
      console.log(Object.keys(anObj)); //['a', 'b', 'c']

      const str = 'abc';
      console.log(Object.keys(str)); //['a', 'b', 'c']
    </script>
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